Heat exchanger

ABSTRACT

A heat exchanger includes a central chamber, having a proximal end and a distal end. A return manifold is connected to the distal end of the central chamber. A plurality of tubes, are positioned around the central chamber. An exhaust manifold receives the tubes and includes an exhaust vent. The central chamber is insulated for the portion within the exhaust manifold.

TECHNICAL FIELD

[0001] The present invention relates generally to heat exchangers.

BACKGROUND OF THE INVENTION

[0002] Heat exchangers are typically used to transfer heat from one fluid to another fluid. A common example of a heat exchanger is the radiator in a car which is used to cool the internal engine coolant. Hot engine coolant is pumped into the car's radiator, while at the same time ambient air passes over the radiator which cools the engine coolant. As such, heat is transferred from the engine coolant to the ambient air. Heat exchangers are also used to heat fluids. For instance, many industrial settings require heated tanks of liquids. Heat exchangers using gas powered burners are immersed in the tank which then heat the liquids within the tank. Recent improvements in heat exchanger technology are detailed in U.S. Pat. No. 6,296,050 (hereby incorporated by reference in its entirety). The '050 patent employs hybrid heat transfer. The main tube utilizes traditional flame to tube to water heat transfer, whereas the smaller return tubes utilize high velocity air to tube to water heat transfer.

SUMMARY OF THE INVENTION

[0003] An object of the invention is to provide an improved heat exchanger. Additional objectives, advantages and novel features of the invention will be set forth in the description that follows and, in part, will become apparent to those skilled in the art upon examining or practicing the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.

[0004] One aspect of the present invention is a heat exchanger comprising a central chamber having a proximal end and a distal end. A first manifold is connected to the distal end of the central chamber. A first plurality of straight tubes each having a proximal end and a distal end are connected to the first manifold at the distal end. The straight tubes are positioned around the central chamber in a first circumferential pattern. A second manifold is connected to the proximal ends of the straight tubes and has an exhaust vent. A first flange is connected to the proximal end of the central chamber for mounting a heat transfer fluid source to the central chamber. The central chamber is insulated from the first flange to the second manifold in such a way as to minimize heat loss to the exhaust vent.

[0005] Another aspect of the present invention is a heat exchanger comprising a central chamber having a proximal end and a distal end. A first manifold is connected to the distal end of the central chamber. A first plurality of straight tubes each having a proximal end and a distal end are connected to the first manifold at the distal end. The straight tubes are positioned around the central chamber in a first circumferential pattern. A second set of tubes are positioned in a second circumferential pattern around the central chamber. A second manifold is connected to the proximal ends of the straight tubes and has an exhaust vent. A first flange is connected to the proximal end of the central chamber for mounting a heat transfer fluid source to the central chamber. The central chamber is insulated from the first flange to the second manifold in such a way as to minimize heat loss to the exhaust vent.

[0006] Still another aspect of the present invention is a heat exchanger for heating a fluid in a container. The heat exchanger has a flange sealingly mounted to the container. A center tube, immersed in the fluid, has a proximal end and a distal end. A return manifold is connected to the distal end of the center tube and is immersed in the fluid. A first set of straight tubes are positioned in a circumferential pattern at a first radius around the center tube and parallel to the center tube. Each of the first set of tubes have a proximal end and a distal end connected to the return manifold. A second set of straight tubes are positioned in a circumferential pattern at a second radius around the center tube and parallel to the center tube. Each of the second set of tubes have a proximal end and a distal end connected to the return manifold. The first and second sets of straight tubes are immersed in the fluid in the container. An exhaust manifold is connected to the proximal end of the first and second sets of tubes around the center tube. The exhaust manifold has a vent located outside the container. A flange is connected to the proximal end of the center tube which extends outside the container and exhaust vent. The center tube is insulated from the flange to the exhaust manifold in such a way as to minimize heat loss to the exhaust vent.

[0007] Still other aspects of the present invention will become apparent to those skilled in the art from the following description of a preferred embodiment, which is by way of illustration, one of the best modes contemplated for carrying out the invention. As will be realized, the invention is capable of other different and obvious aspects, all without departing from the invention. Accordingly, the drawings and descriptions are illustrative in nature and not restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The accompanying drawings, incorporated in and forming part of the specification, illustrate several aspects of the present invention and, together with their descriptions, serve to explain the principles of the invention. In the drawings:

[0009]FIG. 1 illustrates a side view of one embodiment of a heat exchanger connected to an immersion tank;

[0010]FIG. 2 illustrates a cross-sectional view of the heat exchanger depicted in FIG. 1;

[0011]FIG. 3 illustrates one embodiment of a heat exchanger being used for extraneous heating of a fluid;

[0012]FIG. 4 illustrates one embodiment of a heat exchanger being used to heat air; and

[0013]FIG. 5 illustrates a side view of one embodiment of a heat exchanger connected to an immersion tank.

[0014] Reference will now be made to one embodiment of the invention, an example of which is illustrated in the accompanying drawings, wherein like numerals indicate the same element throughout the views.

DETAILED DESCRIPTION

[0015] One embodiment of the present invention is depicted in FIG. 1. This embodiment is using in conjunction with an immersion tank 10 which contains a fluid 13, such as water. One with ordinary skill in the art will readily appreciate that the present invention can be used in other applications and further can be used to heat or cool any fluid, whether it be a liquid or gas. For the purposes of illustration, the fluid 13 in this embodiment is contained by the immersion tank 10 and is filled to the fluid level 14. The immersion tank 10 includes a tank wall 11 having an opening 12 which receives the heat exchanger.

[0016] The heat transfer fluid source 20 provides a source of the gases or liquids which are used to heat or cool the fluid 13. In one exemplary embodiment, a small bore burner technology, such as forced draft IMMERSOJET BURNERS from Eclipse Combustion of Rockford, Ill. or induced draft TYPE CX burners from Power Flame of Parsons, Kans. are implemented. Small bore immersion technology burners are specifically configured to produce very short flames, usually contained within the burner housing outside the tank, which provide very hot, high velocity exhaust gases to transfer heat to the inner immersion tube wall and then to the bath. Small bore immersion tubes typically are much smaller in diameter than traditional immersion burner units and typically efficiencies of 80%-85% are achieved. The smaller diameter tubes can also lead to increased design flexibility and lower costs. Naturally, any other source of heated gas could alternatively be used, including for instance, electric resistance heating, heated gases from an external source such as steam or escaping gases from a separate system, and the like. Other heat transfer fluids such as steam, synthetic organic/silicone fluids and inhibited glycol fluids can be utilized in place of combustion gases in the present invention. Exemplary fluids include, DOWTHERM A, SYLTHERM 800, DOWTHERM G, DOWTHERM RP, DOWTHERM HT and DOWTHERM MX heat transfer fluids from the Dow Chemical Company of Midland, Mich.

[0017] The heat transfer fluid source 20 is connected to the heat exchanger by the flange 21, which is joined to flange 64. The flange 64 is dimensioned such that it is capable of receiving a variety of differently sized heat transfer fluid sources. The central tube 30 is positioned within the exhaust manifold 60.

[0018] The central tube 30 provides a chamber within which fluids from the heat transfer fluid source 20 are delivered. The central tube 30 has a proximal end 31, a distal end 32, and a flowpath 33 extending between the two ends 31, 32. The central tube 30 can take a variety of different shapes and sizes. For instance, one exemplary embodiment has a central tube 30 made of a 3 inch diameter steel tubing, preferably carbon steel or stainless steel, and is about 61 inches in length. The heat exchanger is constructed from materials known to one of ordinary skill in the art, such as the selection of the appropriate grade of carbon and/or alloy steels depending upon the application. For example, heating wash water to 180° F. may require carbon steel construction, whereas heating a food product may require stainless steel construction.

[0019] Attached to the distal end 32 of the central tube 30 is a return manifold 40. In one embodiment of the present invention, the return manifold is made of the same material as the center tube 30 and is joined by a process such as welding or brazing. Alternatively, in another embodiment of the present invention, the return manifold 40 could be fastened to the central tube 30, such as with a flange, or integral to the central tube 30, such as a formed or cast portion. The return manifold 40 is immersed in the fluid 13 such that the outer surface 41 is wetted, therefore providing another heat transfer surface.

[0020] A plurality of return tubes 50 are positioned around the central tube 30. In an exemplary embodiment, the return tubes 50 are straight and are positioned in a circumferential pattern about the central tube 30. As best illustrated in FIG. 2, one embodiment of the invention includes two circles of return tubes 50 positioned at a first radius 54 and a second radius 55 around the central tube 30. In other embodiments, three or more circles of return tubes can be implemented. In one embodiment, the return tubes 50 are evenly spaced relative to one another.

[0021] Each return tube 50 includes a proximal end 51, a distal end 52, and a flowpath 53 extending between the two ends 51, 52. The distal ends 52 are coupled to the return manifold 40. In one embodiment, the distal ends 52 are coupled to the return manifold 40 in the same manner that the central tube 30 is coupled to the return manifold 40. In an exemplary embodiment, the return tubes 50 are made of the same material as the central tube 30 and the return manifold 40. One believed advantage of straight return tubes 50 is that connection stresses with the return and exhaust manifolds 40, 60 will tend to be uniform. Additional believed advantages of straight return tubes 50 are that they are easy to manufacture, do not require a bending operation, and are less likely to be fouled with dirt. As shown in the embodiment of FIG. 1, the return tubes 50 are immersed in the fluid 13 such that the outer surface 56 is wetted, therefore providing another heat transfer surface. Optionally, the return tubes 50 are approximately the same length as the central tube 30 and are positioned parallel to the central tube 30.

[0022] The exhaust manifold 60 is connected to the proximal ends 51 of the return tubes 50. The exhaust manifold 60 includes an exhaust vent 61, which is coupled to a flue 62 through which gases are vented. An optional tank flange 63 is coupled to the exhaust manifold 60 and joined to the tank wall 11 to provide structural support to the heat exchanger. The flange 63 is positioned relative to the exhaust manifold 60 such that a portion of the exhaust manifold 60 is wetted by the fluid 13 thus providing another heat transfer surface. Preferably, a seal or gasket (not shown) is positioned between the flange 63 and the tank wall 11 so as to provide a fluid-tight seal. A variety of mechanisms can be used to attach the tank flange 63 to the tank wall 11, such as bolts, screws, a threaded coupling, interference fit, welds, and the like.

[0023] In operation, heated gases or liquids exit the heat transfer fluid source 20 into the flowpath 33. As illustrated by the flow arrows, the heated gases or liquids move toward the distal end 32 of the central tube 30 and into the return manifold 40. The gases or liquids then enter the distal ends 52 of the various return tubes 50 and traverse towards the proximal ends 51. The gases or liquids then enter the exhaust manifold 60 flowing around a portion of the central tube 30 and through the exhaust vent 61. The portion of the central tube 30 within the exhaust manifold 60 is insulated with insulation 170 from the exhaust manifold 60 in such a way as to minimize heat loss from the central tube to the exhaust vent and exhaust manifold. In one embodiment, the central tube 30 has insulation 170 from flange 64 to the proximal ends 51 of the various return tubes 50. The gases or liquids then enter the flue 62 and are vented accordingly. One skilled in the art will appreciate the various materials of construction and methods to insulate the portion of the central tube within the exhaust manifold to minimize heat loss to the exhaust event. Such insulation materials include, but are not limited to castable or vacuum formed ceramic fibers. Exemplary vacuum formed ceramic fiber insulation materials include INSWOOL from A. P. Green Co. of Pryor, Ohio and DURABLANKET from Unifrax Co. of Niagara Falls, N.Y. Additional insulation materials include rock wool, fiberglass, cellulose, thermofiber, polystyrene, and polyisocyanurate insulation or mixtures thereof. In another exemplary embodiment, the insulation is wrapped with a stainless steel skin. The stainless steel skin prevents erosion of the insulation materials and potential degradation of properties by liquid contact.

[0024] One advantage of the embodiment depicted in FIG. 1 is that the heat exchanger has a relatively large heat transfer surface including the multiple rows of return tubes 50, the return manifold 40, the central tube 30, and the exhaust manifold 60. The relatively high heat transfer surface results in a more efficient heat exchanger and lower exit gas or liquid temperatures. Further, the relatively large heat transfer surface results in lower surface temperature, which can be desirable for temperature sensitive fluids or fluids which may tend to cake on hot surfaces.

[0025]FIG. 3 illustrates an embodiment of the invention being used as an instantaneous fluid heater. The heat exchanger, shown in phantom, is inserted in the housing 70, which is preferably insulated. The flange 21 is coupled to the mating flange 78, thereby resulting in a fluid-tight seal with the housing 70. Fluid, whether it be a liquid or gas, enters the housing 70 through the inlet 72 and exits through the outlet 74. The fluids flow between the inlet 72 and outlet 74 circulates over and around the heat exchanger, thereby transferring heat to the fluid. Heat transfer efficiency can be increased by providing a housing 70 dimensioned to closely fit the heat exchanger, and further improve by including optional baffles 76, which result in additional fluid mixing within the housing 70.

[0026]FIG. 4 illustrates an embodiment of the invention being used as a process air heater. Two or more heat exchangers are positioned within the duct 80. Forced air enters the duct 80 through the inlet 82 and circulates over and around the heat exchangers thereby heating the air. The heated air then exits the duct 80 through the outlet 84, which is then used accordingly. One with ordinary skill in the art will readily recognize that similar configurations can be used to heat any gas and is not limited to air.

[0027] Another embodiment of the present invention is depicted in FIG. 5. In operation, heated gases or liquids exit the heat transfer fluid source 20 into the flowpath 33. As illustrated by the flow arrows, the heated gases or liquids move toward the distal end 32 of the central tube 30 and into the return manifold 40. The gases or liquids then enter the distal ends 52 of the various return tubes 50 and traverse towards the proximal ends 51. The gases or liquids then enter the exhaust manifold 60 flowing around a portion of the central tube 30 and through the exhaust vent 61. The portion of the central tube 30 within the exhaust manifold 60 is jacketed with an annular tube 180. The annular tube 180 is in fluid communication with the fluid 13 in the tank 10. In an exemplary embodiment, fluid 13 is contained between the annular tube 180 and the central tube 30 for the portion within the exhaust manifold 60. In one embodiment, the annular tube jacketing the central tube comprises an annular tube from flange 64 to the proximal ends 51 of the various return tubes 50. In another exemplary embodiment, the fluid 13 contained between the annular tube 180 and the central tube 30 is circulated. One skilled in the art will appreciate the various materials of construction and methods to insulate the portion of the central tube within the exhaust manifold to minimize heat loss to the exhaust event. Such insulation materials include, but are not limited to castable or vacuum formed ceramic fibers. Exemplary vacuum formed ceramic fiber insulation materials include INSWOOL from A.P. Green Co. of Pryor, Ohio and DURABLANKET from Unifrax Co. of Niagara Falls, N.Y. Additional insulation materials include rock wool, fiberglass, cellulose, thermofiber, polystyrene, and polyisocyanurate insulation or mixtures thereof. In another exemplary embodiment, the insulation is wrapped with a stainless steel skin. The stainless steel skin prevents erosion of the insulation materials and potential degradation of properties by liquid contact.

[0028] The foregoing description of the preferred embodiment of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive nor to limit the invention to the precise form disclosed. Many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the above teaching. Accordingly, this invention is intended to embrace all alternatives, modifications, and variations that fall within the spirit and broad scope of the amended claims. 

We claim:
 1. A heat exchanger, comprising: a) a central chamber having a proximal end and a distal end; b) a return manifold connected to the distal end of the central chamber; c) a first plurality of straight tubes each having a proximal end and a distal end connected to the return manifold, said first plurality of straight tubes being arranged in a first circumferential pattern around the central chamber; and e) an exhaust manifold connected to the proximal ends of the straight tubes, said exhaust manifold having an exhaust vent; wherein a portion of the central chamber passes through the exhaust manifold and further wherein the portion of the central chamber passing through the exhaust manifold is insulated in such a way as to minimize heat loss to the exhaust manifold.
 2. A heat exchanger, comprising: a) a central chamber having a proximal end and a distal end; b) a return manifold connected to the distal end of the central chamber; c) a first plurality of straight tubes each having a proximal end and a distal end connected to the return manifold, said first plurality of straight tubes being arranged in a first circumferential pattern around the central chamber; d) a second plurality of straight tubes each having a proximal end and a distal end connected to the return manifold, said second plurality of straight tubes being arranged in a second circumferential pattern around the central chamber; and e) an exhaust manifold connected to the proximal ends of the straight tubes, said exhaust manifold having an exhaust vent; wherein a portion of the central chamber passes through the exhaust manifold and further wherein the portion of the central chamber passing through the exhaust manifold is insulated in such a way as to minimize heat loss to the exhaust manifold.
 3. A heat exchanger as recited in claim 2, wherein the central chamber is a tube.
 4. A heat exchanger as recited in claim 3, wherein the straight tubes are parallel with the central chamber tube.
 5. A heat exchanger as recited in claim 2, further comprising a heat transfer fluid source.
 6. A heat exchanger as recited in claim 5, wherein the heat transfer fluid source comprises a small bore immersion burner.
 7. A heat exchanger as recited in claim 2, further comprising a flange for mounting the heat exchanger to a tank.
 8. A heat exchanger as recited in claim 5, wherein the heat transfer fluid sources comprises a heat transfer fluid.
 9. A heat exchanger as recited in claim 8, wherein the heat transfer fluid comprises steam.
 10. A heat exchanger as recited in claim 8, wherein the heat transfer fluid comprises synthetic organic fluids, silicone fluids or mixtures thereof.
 11. A heat exchanger as recited in claim 2, wherein the insulation portion of the central chamber is on the exterior of the central chamber.
 12. A heat exchanger as recited in claim 2, wherein the insulated portion of the central chamber is on the interior of the central chamber.
 13. A heat exchanger as recited in claim 2, wherein the insulated portion of the central chamber comprises a ceramic fiber blanket.
 14. A heat exchanger as recited in claim 13, wherein the insulated portion of the central chamber further comprises a stainless steel skin over the ceramic fiber blanket.
 15. A heat exchanger for heating a fluid in a container, the heat exchanger comprising: a) a flange sealing mounted to the container; b) a center tube having a proximal end and a distal end, said center tube being immersed in the fluid; c) a return manifold connected to the distal end of the center tube, said return manifold being immersed in the fluid; d) a first set of straight tubes each having a proximal end and a distal end connected to the return manifold, said first set of tubes being positioned in a circumferential pattern at a first radius around the center tube and parallel to the center tube, said first set of tubes being immersed in the fluid; e) a second set of straight tubes each having a proximal end and a distal end connected to the return manifold, said second set of tubes being positioned in a circumferential pattern at a second radius around the center tube and parallel to the center tube, said second set of tubes being immersed in the fluid; f) an exhaust manifold connected to the proximal ends of the first and second sets of tubes, said exhaust manifold having a vent located outside the container; g) a heat transfer fluid source capable of producing heated fluids connected to the proximal end of the center tube; wherein a portion of the central tube passes through the exhaust manifold and further wherein the portion of the central tube passing through the exhaust manifold is insulated in such a way as to minimize heat loss to the exhaust manifold; and h) a flowpath for heated fluids extending from the heat transfer fluid source to the distal end of the center tube, to the return manifold, to the distal ends of the first and second sets of the tubes, to the proximal ends of the first and second sets of the tubes, to the exhaust manifold, to the vent.
 16. A heat exchanger as recited in claim 15, wherein the first set of straight tubes are equally spaced relative to one another.
 17. A heat exchanger as recited in claim 15, wherein the second set of straight tubes are equally spaced relative to one another.
 18. A heat exchanger as recited in claim 15, wherein the heat transfer fluid source comprises a small bore immersion burner.
 19. A heat exchanger as recited in claim 15, wherein the central tube is insulated with a ceramic fiber blanket.
 20. A heat exchanger as recited in claim 19, further comprising a stainless steel skin over the ceramic fiber blanket.
 21. A heat exchanger for heating a fluid in a container, the heat exchanger comprising: a) a flange sealing mounted to the container; b) a center tube having a proximal end and a distal end, said center tube being immersed in the fluid; c) a return manifold connected to the distal end of the center tube, said return manifold being immersed in the fluid; d) a first set of straight tubes each having a proximal end and a distal end connected to the return manifold, said first set of tubes being positioned in a circumferential pattern at a first radius around the center tube and parallel to the center tube, said first set of tubes being immersed in the fluid; e) a second set of straight tubes each having a proximal end and a distal end connected to the return manifold, said second set of tubes being positioned in a circumferential pattern at a second radius around the center tube and parallel to the center tube, said second set of tubes being immersed in the fluid; f) an exhaust manifold connected to the proximal ends of the first and second sets of tubes, said exhaust manifold having a vent located outside the container; g) a heat transfer fluid source capable of producing heated fluids connected to the proximal end of the center tube; wherein a portion of the central tube passes through the exhaust manifold; h) an annular tube jacketing the portion of the central tube passing through the exhaust manifold; wherein the annular tube is insulated in such a way as to minimize heat loss to the exhaust manifold; and i) a flowpath for heated fluids extending from the heat transfer fluid source to the distal end of the center tube, to the return manifold, to the distal ends of the first and second sets of the tubes, to the proximal ends of the first and second sets of the tubes, to the exhaust manifold, to the vent. 